Timer for electronic ovens and the like



United States Patent Ronald M. Bassett Chicago, Ill.

[21] AppLNo. 821,442

[22] Filed May 2,1969

[45] Patented Dec.15,l970

[73] Assignee International Register Company Chicago,lll.

a corporation of Illinois [72] Inventor [54] TIMER FOR ELECTRONIC OVENS AND THE LIKE 24 Claims, 16 Drawing Figs.

[52] [LS-Cl. 200/3 200/39; 219/493; 74/352 [51] Int. Cl ..1'101h 43/10 [50] Field ofSearch 74/3.52, 3.54, 3.56, 3.50, 568T; 219/1055, 492, 493; 200/38, 34(lnquired), 39

so 8 References Cited UNITED STATES PATENTS 2,605,833 8/1952 Bliss zoo/39m) 2,733,764 2/1957 Bliss 200/39 2,783,835 3/1957 Poole ZOO/39(R) 2,837,621 6/1958 Lux et al. 200/39(R)X 3,038,040 6/1962 Stolle et a1 200/39(R)X 3,124,668 3/1964 Zagorski et al. ZOO/39X 3,286,924 11/1966 Banathy 219/493X Primary Examiner-Robert K. Schaefer Assistant Examiner-J. R. Scott Attorney-Robert R. Lockwood ABSTRACT: A dual speed timer controls accurately timewise the closing and opening of one or more switches during a time interval by a cam or cams nonrotatably mounted on a relatively endwise movable time interval shaft that is driven at either a relatively high or a relatively low speed by a timer motor through high or low-speed gears depending upon the manually endwise preset position of the time interval shaft. A latch cam, nonrotatably secured to the shaft, holds it in the low-speed position until near the end of the interval. A buzzer is operated to signal the end of the interval. The switches are sequentially PATENTEDUEBI'SISYB 8548126 SHEET 2 UF 4 105 joq 74 PATENTED nun 519m SHEET 3 [IF 4 PATENTEU UECI I976 I v- O ELECTRONIC MI W VE MICROWAVE Z A OVEN GE ERATOR ATCH CAM OVEN CAM MOTOR CAM TIMER FOR ELECTRONIC OVENS AND THE LIKE When cooking of foodstuff is accomplished in an oven heated by microwave energy, only a relatively short time is required to complete the cooking cycle. The'maximum time required ordinarily does not exceed 20 minutes. For some foodstuff the maximum time required may not exceed 5 minutes and often is substantially less-It is desirable to set accurately the time interval in small increments such as minutes and/or fractions of minutes. The microwave energy is generated by conventional electronic equipment which requires some degree of cooling to prevent excessive temperature rise in it. A preferred cycle of operation includes energizing the cooling mechanism for the microwave generatonfor example the motor of a cooling fan, and then energizing the microwave generator to start the cooking process. At the expiration of a predetermined interval, which may be of the order of l or more minutes and/or a fraction of a minute, the microwave generator ceases to operate, the cooling mechanism continues to operate for a short interval and a signal provided by a buzzer is operated during this interval to indicate that the cooling cycle has been completed. Then both the coolingmechanism and the signal cease to operate.

According to this invention individual switches are provided for controlling the motor of the fan for the cooling mechanism and for controlling the operation of the microwave generator. Cams, nonrotatably mounted with respect to a relatively endwise slidable time interval setting shaft, individually control the two switches in timed sequence. The time interval setting shaft is driven by a timer motor at a relatively low speed for an interval setting, for example, up to 20 minutes and at a relatively high speed for an interval setting, for example, up to'5 minutes. The interval range is interval determined by the endwise position of the time interval-setting shaft. When it is pulled out, a gear secured thereto is driventhrough a reduction gear train at the relatively low speed. On inward movement of the shaft, the gear is shifted to mesh with a higher speed part of the reduction gear train. A latch cam, rotatable with the gear, holds it in the low-speed position against the biasing action of a spring which urges the gear to the highspeed position. A spring operated latch holds the latch cam in the low-speed position until near the end of the low-speed cycle whereupon the cam is released and'the gear is shifted to the high-speed position. Shortly thereafter the switch controlling the microwave generator is opened followed by operation of the signal buzzer. Then the switch controlling the motor of the cooling fan and the timer motor is opened and the buzzer ceases to operate.

For the high-speed cycle, the time interval setting shaft remains in the inner position with a corresponding lesser time being required to return it to the initial portion of the adjustable time cycle.

A dial, rotatable with the time interval setting shaft relative to an index, has two .sets of time interval markings thereon. One of them is from to minutes for the high-speed short time interval while the other is from 0 to minutes for the low-speed long time interval. In either position of the time in terval setting shaft, it is rotated in one direction with the dial relative to the index to the desired time interval marking. The buzzer is rendered inoperative and the fan motor and timer motor are energized by closure of the switch for the fan motor. Subsequently the other switch is closed to energize the oven. The timer motor then rotates the dial and the time interval setting shaft in a reverse direction to effect the control functions at the end of either preset interval.

A fail safe feature is incorporated in the timing mechanism and over cooking is avoided should the time interval shaft be accidentally moved inwardly from the low-speed position. When this occurs, the latch holding the latch cam is unlatched and a shorter cooking interval is automatically provided. The timer then can be reset, taking into account the cooking time that already has elapsed.

A wide variation in the ratio of the high speed to the low speed can be obtained by employing different gear assemblies in the reduction gear train driven by the timer motor. Each gear assembly comprises two gears having different numbers of teeth and arranged to rotate about centers correspondingly differently spaced from a pinion driven at a constant speed by the timer motor. Thus it is possible to obtain, in addition to the speed ratio of 5 to 20, speed ratios of 5 to- 30 and 5 to 60. By reducing the speed of the motor driven pinion by one half, ratios of 10 to 40, 10 to 60 and 10 to can be obtained.

While a particular application of the herein disclosed timer is in connection with a microwave oven which must be accurately timed, it can be used also for timing photographic developing processes and the like requiring relatively long and short time intervals measured with a high degree of precision.

In the drawings:

FIG. 1 is a top plan view of a dual speed timer in which this invention is embodied, the timer being shown in the lower speed position.

FIG. 2 is a front view of the timer shown in FIG. 1.

FIG. 3 is a view in side elevation, looking from right to left of FIG. 2.

FIG. 4 is a view in side elevation looking from left to right of FIG. 2.

FIG. 5 is a view, in rear elevation, of the timer shown in the preceeding FIGS.

FIG. 6 is a bottom plan view of the timer shown in FIG. 5.

FIG. 7 is an exploded view,at an enlarged scale, of the dial, shaft, cam and latch. 1

FIG. 8 is a sectional view, at an enlarged scale, showing the cams and mounting thereof on the time interval setting shaft.

FIGS. 9 and 10 are vertical, sectional views taken generally along lines 9-9 and 10-10, respectively, of FIG. 8.

FIG. 11 is a vertical sectional view taken generally along line 11-11 of FIG. 8, the motor shut off cam having been rotated to the OFF" position.

FIG. 12 is a plan view of the reduction gear set employed in the timer shown in the preceding figures and arranged to provide for the time interval settings of 0-5 or O-2O minutes.

FIG. 13 is a view, similar to FIG. 12, with gear ratios for 0- -5 and 0'30 minutes.

FIG. 14 is a view, similar to FIG. 12, and arranged to provide a gear ratio for 0 -5 and 0-60 minutes.

FIG. 15 is a view, in front elevation, of the backplate for the timer.

FIG. 16 shows diagrammatically the circuit connections that can be employed for the timer disclosed herein.

In FIGS. 16 there is indicated, generally at 10, a dual high speed timer embodying this invention. It comprises a metallic frame that is indicated, generally, at II which includes a front plate 12, an intermediate plate 13 and a backplate 14 which is provided with a rearwardly extending flange 15. Plate mounting studs 16, three in number, and a relatively short plate mounting stud 17 serve to hold the plates 12, 13 and 14 in rigid spaced relation. The timer 10 can be mounted on various supports and can be positioned as shown in FIG. 2 or it can be positioned vertically rather than horizontally. For illustrative purposes a panel 18 is indicated by broken lines on which the timer 10 can be mounted. Spacers 19 are interposed between the front plate 12 and the rear side of the panel 18 while screws 20 serve to secure the timer 10 in position. The front plate 12 carries an index 21 with respect to which a dial 22 is arranged to rotate. If the timer 10 is mounted on the panel 18, then the index 21 is mounted thereon. As indicated, the timer 10 can be positioned vertically in which case the index 21 would be located at the top rather to one side.

The dial 22 is secured to a time interval shaft 23 and is arranged to be rotated manually by a knob 24. The dial 22 is provided with two sets of minute markings along its periphery, one set, indicated at 25, is from 0-5 minutes while the other set, indicated at 26, if from 0-20 minutes. Depending upon the 'endwise position of the shaft 23, it requires either 5 minutes or 20 minutes for the dial 22 to be rotated from a position with the maximum setting in registry with the index 21 to the zero position. Subsequently the dial 22 continues to first or motor switch 30 with a snap action.

be driven until an OFF marking 27 registers with the index i rotation of the cam bushing 36 and parts mounted thereon is In FIGS. 1, 4, 6 and 16 there is shown a first or motor switch 30 and a second or oven switch 31 thefunctions of which in a circuit will be described hereinafter. The switches 30 and 31 are of the *micro" type and normally are biased to the open position. The arrangement is such that'the, first or motor switch 30 is closed first and opened last and the second or oven switch 31 closes last and opens first. For operating the switches 30 and 31 a first or motor switch lever 32 and a second or oven switch lever 33 are associated with the,

srnbly, indicated generally at 35.

As shown in FIGS. 7 and 8, the cam assemblies 34 and 35 are mounted on a cam bushing 36 in which the time interval shaft 23 is rotatably and endwise slidably' mounted. One end 37 of the cam bushing 36 is journaled in the front plate 12. The other-end is recessed, as indicated at 38, to receiveone end of a coil compression spring 39 which surrounds the shaft 23. At its other end the spring 39 bears againsta latch cam 40 which is secured to a cam and gear bushing 41. The cam and gear bushing 41 is secured at42 to the shaft 23 so that it rotatesand moves endwise therewith. Adjacent the cam and gear bushing 41 is a bearing 43 which is mounted on the backplate 14 and held in position thereon by a retaining spring wire 44.

. The first or motor switch cam assembly 34, FIGS. 7 and 8 comprises a wiper cam 46 that is secured to one end of the cam bushing 36 and .a motor shutoff cam 47 that is rotatably mounted'on the cam bushing 36. Arcuate slots 48 and 49 are formed in the earns 46 and 47 forreceiving hooked ends 50 of a, single turn spring 51 which extends around the cam bushing 36. The spring 51 biases the motor shutoff cam 47 to a position in which the arcuate slots 48 and 49 are in registry and permits a slight'degree of relative rotation. The wiper cam 46 has a transverse'cam surface 52 for moving the first or motor switch lever 32 to close the first or" motor switch 30. The motor shutoff cam 37 has a radial cam surface 53 which permits, at the end of the present time interval, movement of the first or motor switch lever'32 radially inwardly to open the The second or oven. switch cam assembly 35 is similar in construction to that of the first or motor switch cam assembly effected with the time interval shaft 23.

Secured and rotatable with the cam and gear bushing 41, which is secured at 42 to the time interval shaft 23, is a driven gear 71. As shown in FIGS. 1, 3, 4', 6 and 12, the gear 71 isarranged to have driving engagement with either a relatively low-speed pinion 72 or a relatively high-speed pinion 73, de-

pending upon the endwise position of the time interval shaft respondingly different time intervals. v

23. The relatively high-speedpinion 73 can be driven through to which is secured a relatively large diameter gear 77 which meshes with the pinion 73. Also secured'to the shaft 76 is a relatively small diameter gear 78 which meshes with a large diameter gear 79 that drives the pinion 72 through a suitable clutch.

The ends .80 of the shaft 76 are journaled in openings in the intermediate plate 13 and backplate 14. The openings in the backplate 14 are indicated at 81 in FIG. 15. As will appear hereinafter, by employing different sizes of gears for the-idler gear assembly 75 and different sizes of large diameter gears for the gear 79,- it is possible to utilize the driven gear 71- and pinions 72 and 73 without change to obtain different time intervals for returning thedial 22 to the zero position while effecting operation of Y the switches 30 and 31 for cor The time interval shaft 23 is biased by the spring 39 to maintain the driven gear 71 in engagement with the relatively highspeed pinion 73. It is necessary-to move the time interval shaft 23 endwise against the biasing action of the spring 39 to position the driven gear 71 in engagement with the relatively lowspeed pinion 72. In order to hold the driven gear 71 in engagement with the relatively low-speed pinion 72 there is provided a latch 85, FIGS. 3 and 7, which is in the form of a flat metallic plate. The latch 85 is positioned between the front plate 12 34. The cam assembly 35 comprises a wiper cam 55 that is secured to the other end of the cam bushing 36. Adjacent the wiper cam 55 is an oven shutoff cam 56 that is rotatably mounted on the cam bushing 36. Arcuate slots 57 and 58 are formed in the cams 55 and 56 to receive the hooked ends 59 of single turn spring 60 which extends around the cam bushing 36 and permits relative movement of the cam 56 with respect to the cam 55. The cam 55 has a transverse cam surface 61 for shifting the second or oven switch lever 33 to close the oven switch 31. A radial cam surface 62 is providedon the shut cam 56 to permit a snap action in the movement of the switch lever 33 to open the oven switch 31. I

It will be recalled that the cam bushing, 36 is rotatably mounted on the time interval shaft 23 which also is movable endwise therethrough. In order to effect rotation of the cam bushing 36 and the cam assemblies 34 and 35 mounted thereon while permitting endwise relative movement of the time interval shaft 23, there is provided a drive pin'65 which is secured at one end at 66 to the wiper cam 55 and is secured at 67 intermediate its ends to the wiper cam 46 while the other end of the drive pin extends into a clearance opening 68 in the latch cam 40. The drive shaft 65 extends through arcuate slots 69 and 70 in the cams 47 and 56 which thereby are permitted to rotate relative to the wiper cams 46 and 55. In this and the backplate 14 in generally parallel radial relation to the time interval shaft 23. The latch has a tooth 86 that is-arranged to engage the rear side of the latch cam 40 to hold it in theposition shown in FIG. 2 and in FIG. 6 in which-the driven gear-71 is in engagement with the relatively low-spe'edpinion 72. One end 87 of the latch 85 is pivotally mounted at 88 in the front plate 12 while its other end 89 is movably mounted in a slot 90, FIG. 15, in the backplate 14. A" coil tension spring 91, FIG. 3,'isanchored at 92 to the front plate 12 and at 93 to the latch 85. The action of the spring 91 is to bias the latch 85' in a counterclockwise direction, about the 'pivotmounting 88 and toward the time interval shaft 23. The latch cam 40 has a notch 94, FIG. 10, in its periphery. As the latch cam 40 approaches the end of the preset time interval with the dial 22 in the relatively long time interval position, the notch 94 comes into registry with the tooth 86 with result that the latch cam 40 no longer is held against the biasing action of the'spring 39. Thereupon the time interval shaft 23 is shifted endwise to place the driven gear 71 in engagement with the relatively high-speed pinion 73 for the remaining part of the preset interval. This insures that the switch cam assemblies 34 and 35 will An inclined surface 97 is formed on the latch 85 between the tooth 36 and the shoulder 85 to permit the latch 85 to be displscedinaclockwisedirection,m.3,whentheknob24 and the dial 22 are moved outwardly to the driven gear-71 in engagementwith the relatively low-speed pinion 72.

'lhe inclined surface 97 permits. displacement of the latch 85 .so that the-toothlCclears-thelatch cam 30'and then the spring 91 pivots the latch 85 to bring the tooth 86 into holding I engagementwith thelatchcsm40.

It is desirable that a signal, audible in nature, be given at the end of the preset time interval. For this purpose, as shown in FIGS. 4, and .6 and 16. there is provided a buzzer arm-100 --which is mountedon a pivot pin 101 thatextends rearwardly frorn'the backplate 14. A- torsion spring 102 surrounds the pivot pin 101 with one end bearing against the buzzer arm 100 while the other end bearsagainstthe underside of the flange 15. The buzzer arm 100 is biased in a counterclockwise 1 direction toward an extension 103 of the magnetic field structure of the synchronous motor 74. An adjusting screw 104 'controls'the sound emitted by 'operationof-the buzzer arm 100 in the magnetic field of the motor 74'. With a view to holding the buzzer arm 100 inthe inoperative position, its'distal'end as is arranged to be engaged'by a distal end 106 of a buzzer. .lift lever 107 which is moun'ted'on a pivot pin 100 that extends rearwardly from the backplate 14. A torsion spring 109 around the pivot pin 1.0 8'acts to bias'thebua'ze'r lift lever 107 in a counterclockwisedirection against a stop pin 110 which extends rearwardly from the backplate 14. Normally the torsion spring 109, acting through the buzzer lift lever 107, holds the buzzer arm 100 in thezin'operative position-shown in FIG. 5. An arm 111 extends-from the .buzzer'liftlever107andjit has .a depending extension 112 provided with an inclined cam s urface 113 that is arranged to be engaged by a detent in the form a of a pin 114 which is carried by the driven gear 71. At the end'of the preset interval, the pin 114'enga'gesthe inclined cam surface 1 13 and, on continued rotation of the driven gear 71, the buuer lift lever 107 is rocked in a'clockwis'e direction to permit the torsion spring 102 to bias'the buzzer arm 100 into operative position with respect the extension 103 of the lnagnetic field structure of themotor74. It continues to vibrate until the motor 74 is deenergizcd. I

In FIG. 16 there is illustrated one application of the use of the-du'sl-high-speed timer previously described. Here conends of the switch levers 32 and 33 to ride along the peripheof the cam auenlblies 34 and 35. The switches and 31 thus are held in the closed positions. Near the end of the preset time interval the radial cam surface 62 on the oven shutoff cam 56 registers with the end of oven switch lever 33.

' 'l'heswitch 31 is opened witha snap action to deenergize the microwave generator 119. The timer; motor 74 continues to drive the cam assemblies 34' and until theradial cam surface 53 on the motor shutoff cam 47 registers with the end of the motor switch lever 32 which thereupon is relcased with a snap action to open switch 30. The energizing circuit to the fan motor 121 is then opened. Also the energizing circuit to the synchronous motor 74 is opened 'on opening of the contacts of the motor switch 30.

With the dial :2 pulled outwardly to opei'ate the timer 10 for the relatively longer time interval, as the latch cam no 'proache's the end of .the time interval the notch registers with the tooth 86 and the latch cam 40no longer is restrained. 'The spring 39 then shifts the time interval shaft 23 to the rear position with the result that the microwave generator 119 and fan motor 121 are sequentially deenergized in the same time interval as for the shorter time interval setting.

. A fail safe feature is provided in dual high-speed timer I 10. When it is'set to operate for the longer time interval, if the high speed timer 10:

FIG. 13 shows a modification of this gearing arrangement in that an idler gear assembly 75' is employed in which a shaft duc'to'rs 1'17 and 118 are indicatedas being energized from a suitable'l20 volt 60.Hz.' source. A microwave generator, indicated generally, at 119 is. arranged to be energizedfrom the conductors 1171and Ill-through. the contacts of the or oven switch 31 to, in turn, energize an electronic microwave oven that is indicated, generally, at 120. For cooling the microwave generator there is provided a fan motor 121 that is energized through the contacts of the first ormotor switch 30 from the conductors 117 and 118 to operate a fan 122 for the purpose of circulating cooling air over the microwave generator 119. While the particular apparatus just described has been illustrated for use in conjunction with the dual highspeed timer 10, it will be understood that other apparatus can be controlled by the switches 30 and 31 for longer or shorter intervalsasmaybedesired. r

. the gears 77',-78' and 79', the ends 80"of the shaft of 76' are In operation. the dial 22 is rotated manually fromthe "OFF." in registry with the index! in scloekwise to the desired time interval setting. lfthe time interval is 5 minuteso'r less, then the dial 2 isrotatedto the dssiredmarkslongtheminutemarkings'udfalongertimeintervalisrcquired,whenthedial22isrotated,itisalsopulled outwsrdlyandisrotatedtothedesiredtimeintervalsetting .sloag the markings 26."1h'e relationship ofthe cams4lsnd55issuchthatthefirstormotorswitch lever32is shifted bythe transverse earn surface 52 to energize the motor 121 before the transverse cam surface '61 shifts the second or oven switch leverv 33 to energize the microwave generator "I. Tll'l insures that the fan '12 2is in operation at thetime that the microwave generator-1'19 is energized. Closure of the first or motor switch 30 also completes an'ener'gizing. circuit for the synchronous motor 74. Continued rotation of the 76 carries a large diameter gear 77 and, a small diameter gear 78., these gears, however, having larger numbers of teeth than the corresponding gears 77 and 78 of the idler gear assembly 75. 'Also a large diameter gear 79 drives the pinion 72 through a suitable clutch. The gear 79' basil-larger number of teeth than the corresponding gear 179 of the idler gear assembly 75. In order, to accommodate the larger diameters of in the intermediate openings one of which is the intermediate opening of the openings 81' in the backplate 14. It

will be understood that there are corresponding'openings-in the intermediate plate 13.'The gearing arrangement shown in FIG. 13 is such as to provide time interval settings of 05 and 0-30 with the pinion 72 being rotated at a speed of one thirty-sixth r.p.m. 1

FIG. 14 shows a still further modification of the reduction gearing between the pinion: 72 and 73.. Here an idler gear assembly 75 is employed having a shah 76" on which a large diameter gear 77" and a small diameter gear 78" are 7 mounted. Also there is provided a large diameter gear 79"which is arranged to drive the pinion 72 through a suitable clutch. The ends 0 0" of the shaft 76" are journaled in openings in the intermediateplate 13 and the backplate 14, the opening 81 in the backplate 14 being the one shown at the left in FIG. 15. This arrangement provides for time interval.

settings wiper cams 46 and 55 in the time setting direction causes the of 0-5 and 0- 60 minutes with the pinion 72 being driven at a speed of one seventy-second r.p.m.

Again it is pointed out that other time intervals can be provided by changing the speed at which the relatively high-speed pinion 73 is rotated. However, in each case no change is required for the driven gear 71 or the pinions 72 and 73.

lclaiml. '1. A dual high-speed timer for controlling the energization of a device requiring accurate timing comprising:

a switch for connecting said device for energiz ation to an electric current source at the beginning of a time interval during which said device is to be energized;

acam for closing and-opening said switchat the beginning and end of said time interval;

a time interval shaft on which said switch cam is nonrotatably and slidably mounted;

a timer motor;

a gear train interconnecting said tirner motor and said time interval shaft including a high-speed gear and a low-speed gear; and i manually operably means for shifting the connection of said time interval shaft from said high-speed gear to said lowspeed gear to effect a corresponding change in the time that said switch is closed by said switch carn.

2. The timer according to claim 1 wherein:

means mount said time interval shaft for endwise movement relative to said switch cam;

a latching cam is secured to said time interval shaft; and

a latch engages said latching cam to hold it and said time interval shaft in one operating position.

3. The timer according to claim 2 wherein means mount said latch for movement to a position to release said time interval shaft in response to endwise movement thereof from said one operating position. I

4. The timer according to claim 2wherein said latching cam is arranged to release said time interval shaft for movement from said one operating position near the end of said time interval to another operating position before said switch cam opens saidswitch.

5. The timer according to claim 1 wherein:

said timer includes a signalling device; and

7 means operated by said time interval shaft initiate operation of said signalling device near the end of said interval.

6. The timer according to claim wherein:

said gear train includes a driven gear secured to said time interval shaft; V

said time interval shaft is-movable endwise relative to said switch cam to shift said driven gear out of engagement with said high-speed gear and into engagement with said low-speed gear; and

said rneansfor initiating operation of said signalling device is carried by said driven gear.

7. The timer according to claim 5 wherein additional means operated by' said time interval shaft deenergize said timer motor and cause operation of said signalling device to cease.

8. The timer accoiding to claim 1 wherein:

said gear train includes a driven gear secured to said time interval shaft; said time interval shaft is movable'endwise relative to said switch cam to shiftsaid driven gear out of engagement with said high-speed gear and into engagement with said low-speed gear;

a latching cam is secured to said time interval shaft; and

a latch engages said latching cam to hold said driven gear in engagement with said low-speed gear. v

9. The timer according to claim 8 wherein said latch is movableto' unlatched position in response to endwise movement of said time interval shaft.

10. The timer according to claim 8 wherein:

s idv timer incl'udes a signalling device; and

adetent carried by said driven gear initiates operation of said signallingdeviceat the end'of said interval.

11. The timer according to claim 8 wherein said latch cam is arranged to be released from said latch near the end of the said time intervalto shift said driven gear into engagement with said high-speed gear before said switch cam opens said switch.

12. The timer according to claim 8 wherein:

means mount said latch for movement along said time interval shaft and laterally away therefrom;

a spring biasessaid latch toward said time interval shaft into latching engagement with said latching cam; and

endwise movement of said time interval shaft from lowspeedto high-speed position is accompanied by movement of saidlatchout of latching engagement with said latching cam. I

13. A dual high-speedtimer for controlling the energization of devices requiring accurate timing comprising:

first and second switches for individually and sequentially connecting devices for energization to an electric current source at the beginning of a time interval during which."

said devices are to be energized;

first and second switch cams for closing and opening said first and second switches'respectively at'pred eterrriined times during said time interval;

a time interval shaft on which said switch cams are nonrotatably and slidably mounted} a timer motor; 'i i a gear train interconnecting said timer motor .and said time interval shaft including a low-speed gear and a high speed gear; and

manually operable means for shifting the connection of said time interval shaft from said highaspeed gear to said lowspeed gear to effect a corresponding .change in the times during'said time interval that said switches are closed by said switchcams.

14. The timer accordingto claim 13 wherein:

means mount said time interval shaft for endwise movement relative to said switch cams;

a latching cam is secured to said time interval shaft; and

a latch engages said latching carn to hold it and said time interval shaft in one operating position.

15. The timer according to claim 14 wherein means mount said latch for movement to a position to release said time interval shaft in response to endwise movement thereof from said one operating position.

16. The timer according to claim 14 wherein said latching camisarranged to release said time interval shaft for movement from 'said one operating position near the end of said time interval to another operating position before said switch cams open the respective switches.

17. The timer according toclaim l3wherein:

. said timer includes a signalling device; and

means operated by said time interval shaft initiate operation of said signalling device near the end of said interval.

18. The timer according to claim 17 wherein:

said gear train includes a driven gear secured to said time interval shaft; said time interval shaft is switch cams to shift said driven gear from engagement with said high-speed gear to engagement with said lowspeed gear; and said means for initiating operation of said signallingdevice is carried by said driven gear.

19. The timer according to claim 17 wherein additional means operated by 'said time interval shaft deenergize said timer motor and cause operation of said signalling device to cease.

20. The timer according to claim 13. wherein:

said gear train includes a driven gear secured to said time interval shaft;

said time interval shaft ismovable'endwise relative to said switch. cams to shiftsaid driven gearout of engagement gear and intoengagement with said 23. The timer according to claim-'13 whereinisaid latching-. cam is arranged to be released from said latch near the end of said time interval to shift said driven gear.into-engagementv with said high-speed gear before said switch cams opens .said switches. I

movable endwise relative tosaid a 3,548,126 9 v r 1 24. The timer acccrding to claim wherein: endwise movement of said time interval shaft from lowmeans mount said latch for movement along said time interspeed to high-speed position is accompanied by moveb n d l g fl away th from; ment of said latch out of latching engagement with said a spring biases said latch toward said time interval shafl: into latching latching engagement with said latching cam; and 5 

